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Saturday, October 20, 2012

Color variation in island strawberry frogs

The strawberry poison frog Oophaga pumilio ranges from Nicaragua through western Panama and throughout most of its mainland range it has a reddish-orange body with blue-black legs, and small black spots on its dorsum. In the Bocas del Toro Archipelago of Panama the frog displays a high level of variation is its warning coloration. More than 15 color morphs are present in the archipelago and include yellow, red, blue, lime green, and bronze morphs as well as others, and the different morphs may occur on the same island. Morphs with spots are also present in the Archipelago, with the size and number of spots varying on the specific morph. The degree of conspicuousness also varies among color morphs in the Bocas del Toro Archipelago. Hegna et al. (2012) used unspotted models of O. pumilio to determine if predation might help explain the color polytypism on Isla Colon in the Bocas del Toro Archipelago of Panama. The authors tested whether attack rates differed among the red mainland morph, green-yellow Isla Colon morph, and a brown colored control. They found that frog color significantly predicted being attacked. The local green Isla Colon models were attacked more than foreign red or brown models. No difference in attack rate were found between red and brown control models. Their results suggest that the red mainland morph possesses a more effective warning signal, even when it is not the local morph. Honest signaling of unpalatability, neophobia, and the use of search images by local predators are potential explanations. Similarity of the brown model to other local poison frogs might explain the lower attack rate compared to previous work. The attack rate was lower on Isla Colon compared to mainland Costa Rica, which supports the hypothesis that less predation in the Bocas del Toro Archipelago may contribute to the overall variation in warning colors in O. pumilio and there by relaxing selection for aposematic traits.

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